1. Field of the Invention
The present invention relates to medical devices, systems, and methods for dilating a cervical canal in a female patient.
2. Description of the Related Art
The cervix is a dense yet distendible organ that responds to internal pressure (within the endocervical canal) by expanding within anatomical limits to assume the diameter or shape of the item causing the pressure. If this pressure is applied gradually, the tissues of the cervix will usually experience minimal damage. It has been observed that if the pressure is maintained for a short period of time, the cervix will temporarily fix itself to that diameter. In other words, the cervix will temporarily stay open even after the pressure has been removed. It will then gradually return to its normal resting diameter of about 3–4 mm.
Since the early 1800s physicians have been attempting to visualize the endometrial cavity through the endocervical canal using a variety of optical instruments. In the late 1800s, Pantaleoni removed a uterine polyp and used silver nitrate to control the bleeding, thereby completing the first successful procedure done through a hysteroscope.
Hysteroscopy, both diagnostic and operative, has come a long way since then, but the fundamental challenges of hysteroscopy have remained unchanged. The two most basic challenges of hysteroscopy are: (1) dilating or opening the cervix in order to permit the insertion of the instrument of choice; and (2) distending the uterine cavity with some form of gas or liquid in order to see and operate.
The first challenge has been addressed in two ways. The first is a series of mechanical dilators that are, for the most part, blunt tipped, tapered metal or plastic rods that are offered in a graduated set of increasing diameters. The mechanical dilators are gently inserted into the cervix starting with the smallest and moving through the larger sizes until the cervix is opened to the desired diameter. Unfortunately, this method can be painful for the patient and often results in tearing of the cervical tissues, which causes bleeding and frequently leads to unintentional perforation of the uterine wall.
Gynecologists recognized the benefits of a more gradual dilation of the cervix and two additional methods were pursued. The first is a seaweed based product called Laminaria and the second is a prostaglandin based drug called Misoprostol also known as Cytotec®, which is manufactured by Pfizer, Inc.
Laminaria is a very thin piece of seaweed that is inserted into the endocervical canal. As the Laminaria absorbs tissue fluid from the body, it swells gradually and dilates the cervix in the process. This method has the benefit of eliminating the pain associated with mechanical dilation and allows the operator to avoid or use minimal mechanical dilation. The problems associated with Laminaria are that it requires an additional visit to the doctor because the medical procedure to be performed must be done between 12 and 24 hours after the insertion of the Laminaria and there is no control of the final dilated diameter of the cervix.
Misoprostol is a drug that has a softening effect of the cervical tissues, allowing cervical dilation with less force. It can be administered either orally or through the vagina. In either case, the patient can administer the drug herself but it does require a trip to the pharmacy. There are however inconveniences associated with the use of Misoprostol. In the case of self-administration, it requires the compliance of the patient and a prescription, and the patient must pick up the prescription from the pharmacy. Since it is a form of prostaglandin, it may also contribute to uterine cramping, which causes pain and discomfort. If the cervix become too soft, establishing a seal on the hysteroscope on the day of the procedure may be problematic. Like all drugs, there can be numerous side effects and complications associated with the use of Misoprostol.
The second and simultaneous effort to address the first challenge of hysteroscopy is to make the instruments smaller, thus requiring a smaller opening of the cervix. This solution does indeed reduce the difficulties and complications mentioned above, but at the cost of a reduction in visual clarity. Additionally, the small instruments that are required for these smaller hysteroscopes are inadequate for all but the most basic procedures a gynecologist performs. These smaller scopes are thus restricted to limited visual diagnostic procedures only.
Since the uterus is only a potential cavity, it needs to be distended in order to see into it, which is the reason for the second basic hysteroscopic challenge. The two primary methods of distension have been and remain to this day to pump gas (usually carbon dioxide) and a fluid of some kind into the uterus. There have been many fluids used for uterine distension over the years, such as physiologic saline, 5% dextrose in water, glycine, sorbitol and others. Each of these solutions and gases carry certain benefits and complications.
All of these distension media do provide at least one common challenge to the hysteroscopist: the need to contain them within the confines of the uterine cavity such that a slight positive intrauterine pressure is established. It is this containment and resultant positive pressure that distends the walls of the uterine cavity, permitting visualization and procedural manipulation by the physician. Typically, the distension media escape past the hysteroscope down the endocervical canal and into the vagina. This loss of fluid not only makes establishing and maintaining a positive pressure difficult, it also allows for a fairly significant volume of contaminated fluid to flow onto the operating room floor. The flow of fluid onto the operation room floor represents a safety hazard for the operating room personnel and if the fluid being used is a non-electrolyte, it also poses a safety risk to the patient. In the latter case, if enough non-electrolytic fluid is absorbed by the patient, it can cause a condition known as hyponatremia, which has a morbidity and mortality risk associated with it. In order to avoid fluid overload, the operating room personnel must carefully monitor how much fluid is introduced into the patient versus how much is recovered, with the net difference assumed to have been absorbed. If fluid is lost to the drapes, floor, etc. this task becomes more difficult and less accurate.